The bulge test is used to determine the presence of fluid in the knee joint. It is useful when only a little fluid is present in the joint.

The suprapatellar bursa is first emptied of fluid by squeezing distally from about 15 cm above the patella. The medial compartment of the knee join is emptied by pressing on the side of the joint with the free hand. The hand is then lifted away and then the lateral side is sharply compressed.
If the test is positive, a ripple is seen on the flattened, medial surface.

The test is negative if the effusion is tense - up to 120 ml.